This invention relates to a method and system for producing purified water, sterile water or a sterile aqueous solution for biological and medical uses. More particularly, this invention relates to a method and apparatus for producing sterile aqueous solutions meeting all user specifications including bacteriological specifications to permit their administration directly or indirectly to a patient.
Conventional water purification systems employing well known technologies such as reverse osmosis, deionization and ultrafiltration are capable of producing chemically and biologically pure water for short periods of time. Generally, when these systems are operated continuously, they will maintain low levels of bacteria and pyrogens for a time period which is dependent upon the temperature at which the system is operated. During system operation, biologically active materials such as bacteria, yeast, mold and pyrogens will begin to proliferate within the system to unacceptably high amounts leading to biological contamination of the normally pure water produced by these systems.
Some conventional systems regain their capacity to produce biologically pure water by rinsing of the systems with sanitizing agents such as formalin or chlorine which control biologic contaminants. While these sanitizing agents perform their function well, they are highly toxic to humans, are difficult to handle and are difficult to rinse out of the purification system. The use of these chemicals has major adverse environmental impact as well.
A second method for insuring biologic purity of water treated with a membrane filter system is to treat the system with a second process which insures the control of all living organisms. One such method is to heat the water with a pasteurization process. However, components within the system such as certain reverse osmosis membranes cannot withstand pasturization temperatures. Therefore, when utilizing a system which is sanitized with high temperature water, undesirable by-pass loops and valves to reverse osmosis units are introduced. Therefore, this method does not clean and sanitize the reverse osmosis unit.
A third method is to pass the purified water through a filter that is capable of filtering from the water all biologically active material. However, this process requires that the initial filtration treatment reduces the bacterial contamination to sufficiently low levels so that the bacterial removal filter does not clog prematurely. This is a very expensive proposition which renders it impractical. Therefore after initial filtration, chemical sanitization agents are still currently required to maintain low bacterial levels in the system.
It has been proposed in U.S. Pat. No. 3,578,774 to provide sterile urological irrigating liquid composition by passing the fluids continuously through a filter designed for removing bacteria. However, this device requires an on site source of nonpyrogenic water and urological fluid. It has also been proposed in U.S. Pat. No. 4,253,457 to prepare such irrigation solutions on site by utilizing a combination of a reverse osmosis unit for removing pyrogens, a deionization unit for removing dissolved solids and pyrogens and a filter for removing bacteria in order to produce pyrogen free, bacteria free solution that can be administered directly to the patient. However, this system is limited since the claim of removing pyrogens by deionization is limited to removal of some pyrogens, but not all, as required for production of bacteria and pyrogen free water. In addition, the system requires chemical sanitization and cleaning; thereby increasing risk to the patient. Neither of the means disclosed in U.S. Pat. Nos. 3,578,774 or 4,253,457 are capable of producing water that meets the USP XXII standards for water for injection or for irrigation for long periods without continuous monitoring, caring and chemical sanitization of the unit by an operator.
British Patent Nos. 1,450,030 and 2,034,584 also disclose means for providing pyrogen free and bacteria free aqueous solution at the site of use of the solutions. However, each of these systems relies upon the use of chemical disinfectant such as with formalin to sanitize the equipment or flash sterilization wherein the water used to form the aqueous solution is heated to a temperature, typically 150.degree. C. to 160.degree. C. The use of chemical sanitization is undesirable even though it is an effective means for killing microorganisms because it also introduces harmful chemicals into the system which can be administered accidentally to the patient. Furthermore, heat sterilization of the water used to form the aqueous solution is undesirable since sterilization is accomplished only in portions of the system exposed to the high temperature. The bacteria and pyrogens continue to multiply in the remaining portion of the system thereby preventing the desired fluid quality from being produced.
U.S. Patent No. 4,610,790 discloses a system for forming USP XX grade water from tap water which includes a carbon-based filtration unit, a reverse osmosis unit, a deionization unit and an ultrafiltration unit. In order to cleanse the system of accumulated microorganisms and pyrogens, the ultrafiltration unit and the deionization unit are flushed with heated water. The reverse osmosis unit is flushed with unheated water and the carbon-based filtration unit is replaced periodically. Since the carbon-based filtration unit and reverse osmosis unit are not exposed to heated water, additional bypass loops and valves must be added to the system. The non-sanitized filter units may eventually produce unacceptable quality product. Furthermore, this system requires a redundant filtration unit for removal of bacteria and pyrogens because the reverse osmosis unit can not be heat sanitized.
Accordingly, it would be desirable to provide a means for producing sterile water which requires minimal care and maintenance, automatically sanitizes and monitors system performance and eliminates chemical sanitization, by-pass loops and redundant filtration steps.